The present invention relates generally to the field of geophysical exploration and more particularly to an improvement in processing and displaying seismic data so as to enhance the evaluation and interpretation of subtle variations in the earth's geological and lithological structures.
In the continuing search for hydrocarbons in the earth, geophysicists seek methods for evaluating and interpreting the effects of geology or lithology on seismic data in order to relate such effects to the occurrence of hydrocarbons. For example, Savit U.S. Pat. No. 3,662,325 discloses a method for displaying both extrinsic and intrinsic properties of subterranean formations which are generated from the seismic data. Using such displays, the geophysicist can infer the geological character of the formation and hence, the probability of locating hydrocarbons. Similarly, Rice in U.S. Pat. No. 4,467,461 discloses an interactive technique for color displaying selected combinations of instantaneous attributes of a seismic signal (e.g., amplitude, frequency, envelope and phase) so as to allow an interpreter to more easily comprehend simultaneous variations of several of the instantaneous attributes and to relate these effects to geophysical occurrences of interest. More recently, Stebens, et al., in U.S. Pat. No. 4,633,399 describes a technique for obtaining the instantaneous phase of a rectified signal to aid in interpreting seismic data. In practice, Stebens, et al., obtains a measure of the absolute value of input seismic data from which they determine its Hilbert transform and then compute a rectified instantaneous phase. Alternatively, Bodine in U.S. Pat. No. 4,633,447 describes a technique for obtaining attributes of a complex signal, unlike the instantaneous attributes of Rice, Savit or Stebens, et al., which describe the mean or dominant character of the seismic signal.
In spite of such advances, a continuing need exists to enhance seismic data so as to better evaluate and interpret subtle variations in the earth's geological and lithological structures, such as, stratigraphic traps, pinchouts and reefs associated with weak faulting structures. Moreover, it is especially important to be able to locate hydrocarbon deposits in regions devoid of strong hydrocarbon indicators, such as bright spots. Responsive to such needs, the present invention describes a novel method for processing seismic data to enhance geophysicists' ability to locate and interpret subtle variations in the earth's geological and lithological structures which can oftentimes be associated with the presence of hydrocarbons.